Solid state shear pulverization and solid state melt extrusion are techniques that may create polymeric materials used in the manufacture of polymer-based goods. Solid state pulverization may produce fine polymeric particulates, while solid state melt extrusion may produce extruded polymeric materials. It may be understood that the solid state melt extrusion process may begin with a solid state pulverization process of the starting materials before the particulates are heated and extruded.
Polymer particulates derived from solid state shear pulverization (hereafter, “SSSP”) may be homo-polymeric (composed of a single polymer or single co-polymer) or hetero-polymeric (composed of multiple types of polymers or co-polymers). Homo-polymeric particulates formed by SSSP techniques may be used to fabricate products or coatings requiring a single type of polymer. In one example, such homo-polymeric particulates may be fabricated from virgin material from a known supplier. Such single-polymeric materials may be required based on the known properties of the polymer and the intended use of the products.
Polylactic acid (hereafter “PLA”), a biologically based and biodegradable polymer that is cost-competitive with petroleum-based polymers, is one non-limiting example of a material that may be processed using SSSP technology. Technological applications of PLA have been limited because of its low thermal stability and toughness. Further, processed PLA may exhibit low crystallinity which may be due at least in part to its slow crystallization rate. As a result, the industrial use of PLA to form semi-crystalline products may be impractical in such processes such as injection molding, in which the cycle times are extremely fast. SSSP processing of PLA has shown to greatly enhance the crystallization kinetics, thereby permitting the production of semi-crystalline products in cycle times common for injection molding.
In some instances, hetero-polymeric particulates may be useful to form products or coatings for which the intended use does not require a single specified composition. Items such as plastic pallets, buckets, and trash bins, for example, may possess certain mechanical requirements but the composition of the items may not be important to their function. It may be understood that such products can be readily and inexpensively produced from unsorted or partially sorted recycled materials.
Additionally, specific combinations of polymer materials with fillers may be desired for improved product properties, such as increased tensile strength and reduced weight. One non-limiting example of a filler material may include rice-husk ash (hereafter, “RHA”), which is mostly composed of silica. A combination of a polymer with RHA may be difficult to process with conventional techniques because RHA is heavily agglomerated. The agglomeration characteristics of RHA may reduce or prevent effective break-up of the RHA particulates and their uniform dispersal within a polymer-RHA composite. The resulting polymer composites may have degraded physical properties such as decreased tensile strength. SSSP has been shown to successfully process polymer-RHA composites at high RHA loadings, resulting in an end product having enhanced hardness and scratch resistance.